Many food products, such as fruit juice, pasteurized or UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material.
The packaging material has a multilayer structure substantially comprising a base layer for stiffness and strength, which may be defined by a layer of fibrous material, e.g. paper, or mineral-filled polypropylene material; and a number of layers of heat-seal plastic material, e.g. polyethylene film, covering both sides of the base layer.
In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of gas- and light-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH) film, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.
As is known, packages of this sort are produced on fully automatic packaging units, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized in the packaging unit, e.g. by applying a chemical sterilizing agent such as a hydrogen peroxide solution, which is subsequently removed, e.g. by heating and evaporation, from the surfaces of the packaging material.
The sterilized web is maintained in a closed, sterile environment, and is folded into a cylinder and sealed longitudinally to form a tube.
The tube is fed in a first vertical direction parallel to its axis, is filled continuously with the sterilized or sterile-processed food product and is heat-sealed at equally spaced cross sections by two pairs of jaws to form pillow packages each having a top and a bottom transverse sealing band, i.e. a band extending along a second direction orthogonal to the first direction.
The tube portion gripped between each pair of jaws is heat sealed by heating means carried by one of the jaws, known as the sealing jaw, and which locally melt the two layers of heat-seal plastic material gripped between the jaws.
For example, packaging material in which the layer of barrier material comprises a sheet of electrically conductive material, e.g. aluminium, is normally heat sealed by a so-called induction heat-sealing process, in which, when the tube is gripped by the two jaws, loss current is induced in, and locally heats, the aluminium sheet, thus melting the heat-seal plastic material locally.
In particular, in induction heat sealing, the heating means substantially comprise an inductor powered by a high-frequency current generator and substantially comprising, in turn, one or more inductor bars made of electrically conductive material, extending parallel to the second direction, and which interact with the tube material to induce a loss current in it and heat it to the necessary sealing temperature.
The heating means are fitted to a sealing element carried by the sealing jaw.
The other jaw, known as the counter-jaw, comprises a counter-sealing element fitted with pressure pads made of elastomeric material, and which cooperate with the inductor bars to heat seal the tube along a relative transverse sealing band.
Furthermore, the counter-jaw houses in sliding manner a cutting element. In particular, the cutting element may slide towards and away from the sealing element of the sealing jaw along a third direction orthogonal to first and second direction.
More precisely, the cutting element is normally maintained in a withdrawn rest position within the counter-sealing element, and is moved into a forward cutting position, in which it projects frontwards from the counter-jaw, engages a blind groove of the sealing element, and cuts along the centreline of the top sealing band of the formed package. In this way, the formed package is separated from the tube.
A need is felt within the industry to avoid the accumulation of residues within the groove of the sealing element. In fact, as it is housed within the groove, the cutting element exerts a force on such residues resulting in the deformation of sealing element of sealing jaw. As a consequence, the life-time of the sealing element of the sealing jaw may be considerably reduced and there could be some risks of damaging the cutting element and/or sealing element, especially in case that sealing element is metallic.
The residues may typically consist of portions of packaging material, in particular paper mixed with polyethylene.
In particular, the aforementioned need is particularly felt when a plurality of opening devices is pre-applied to the tube of packaging material before the heat-sealing of packages and, during the heat-sealing of each package, the relative opening device is housed within a recess arranged in the sealing element of the sealing jaw.
In fact, during the starting cycles of the packaging units, the packaging material may be in an incorrect position with respect to the jaws, when cross sections of tube are heat sealed.
In this case, the opening devices, instead of being housed within the groove of the sealing element may remain, at least partially, along the trajectory of cutting element between the withdrawn rest and the forward cutting position.
In this way, some plastic residues of the opening device may be cut away by cutting element and accumulate into the groove.
As a consequence, even when packaging material has been automatically arranged in the correct position with respect to the jaw, the presence of plastic residues within groove may generate risks of deformation and/or damages of the sealing element of the sealing jaw and/or cutting element.